Conventionally, aluminum bond wire connecting the features of a semiconductor die to the leads of a leadframe in a semiconductor package are bonded directly to the leadframe. The common issues associated when using this method with fine aluminum bond wire (less than about 3 mil diameter) include heel break and bond lift. Heel lift occurs when the bonding parameters are set too high and the bond wire breaks at the bond, potentially resulting in the loss of electrical communication between the semiconductor feature and the lead. Bond lift generally occurs when the bonding parameters are set too low and the bond disengages from the lead. Thus, there is a narrow range of bonding parameters that will result in a resilient bond. Further, the bonding parameters for bonding fine aluminum wire directly to the leadframe are quite sensitive to the material composition of the aluminum wire and the surface condition of the leadframe.
The bond stitch on bump method for bonding gold wires to a leadframe uses a gold bump on the leadframe as the interface between the bond wire and the leadframe. This relaxes the range of bonding parameters for gold bond wires. Other methods may use solder bumps in a similar fashion. However, neither of these methods are suitable for bonding aluminum wire.
There exists a number of U.S. patents directed to wire bonding in semiconductor packaging including U.S. Pat. No. 6,413,797 issued to Oka, et al. on Jul. 2, 2002. Oka teaches a semiconductor device with electrodes having gold bumps disposed thereon in a gold plating process. The gold bumps facilitate the bonding of gold wires to the electrodes. Oka does not teach an inexpensive and simple method of providing an aluminum bump for bonding fine aluminum wire to surfaces.
Therefore, what is desired is a method of bonding fine aluminum wire that has relaxed bonding parameters, that shows improved reliability in reduced heel crack and bond lift situations, and that is inexpensive.